Baler and method of baling

ABSTRACT

A baler including a baling chamber that includes a bale-forming channel including an inlet end and an outlet end, a plunger mounted within the channel for compressing bale material in the channel and driving the compressed bale material towards the outlet end of the channel, and a rotary drive mechanism for driving reciprocating movement of the plunger, and an additional drive mechanism for driving the compressed bale material towards the outlet end of the channel, thereby reducing torque in the rotary drive mechanism.

BACKGROUND OF THE INVENTION

The present invention relates to a baler and a method of baling, inparticular but not exclusively for baling an agricultural crop.

For efficient transport and storage, agricultural products like hay,straw and silage may be compressed into bales of a parallelepiped shape,which are known as ‘square’ bales. After compression of the balematerial the shape and the compression of the bale is maintained bybinding the bale with twines that are looped around the compressed balematerial. The ends of the twine are then knotted together.

Typically, compression of the bale material is performed by areciprocating plunger press baler. A typical baler of this type isdescribed in U.S. Pat. Nos. 4,074,623 and 4,142,746 to HesstonCorporation. This baler includes a pick-up device for picking up balematerial from the ground, a feed device and a baling chamber comprisingan open ended channel through which bale material is forced by areciprocating plunger. The plunger is driven in a linear directionbetween a withdrawn position in front of the baling chamber and anextended position in which it extends into the baling chamber. When theplunger is in the withdrawn position the baling chamber is loaded withthe bale material. The plunger is then driven into the baling chamber sothat this new material is compressed against a body of compressedmaterial already in the baling chamber. The newly compacted material iscalled a ‘wad’. The friction of the compressed material with the wallsof the baling chamber channel provides a resistive force allowing forcompression of the new material that is introduced into the balingchamber in front of the plunger.

After compression, the newly compressed material and the compressedmaterial already in the baling chamber are moved together towards theoutlet end of the baling chamber until the plunger reaches its fullyextended end position. The plunger then moves in the opposite directiontowards its withdrawn position so that the baling chamber can bereloaded with new material to be compressed.

This process is repeated until the body of compressed material in thebaling chamber has reached the required length to form a bale. The bodyof compressed material is then bound with twine, which is knotted by aknotter device. The whole process is then repeated to form another bale.As the new bale is formed the previously formed bale is gradually pushedtowards the outlet end of the baling chamber and is eventually ejectedfrom the chamber.

During the compression stroke, the force exerted by the plungerincreases as the bale material is compressed and typically reaches amaximum value at the moment when the newly entered bale material hasbeen compressed and the bale material already in the channel starts toshift backwards towards the outlet end of the baling chamber. Themaximum value of the plunger force thus depends on the level of frictionbetween the compressed material and the sides of the baling chamber.

The friction within the baling chamber between the compressed materialand the sides of the chamber can be regulated by pressing the sidepanels and/or the top panel of the baling chamber against the compressedmaterial with different levels of force. To avoid damaging the machine,the desired maximum plunger force should not exceed a set valuedetermined by the mechanical design of the machine, but may typicallyrange from, for example, 10% to 100% of the maximum designed plungerforce depending on the required degree of compression.

Typically, the plunger is driven from a rotary drive mechanism or drivetrain that includes a gearbox, a drive shaft and a rotating crank. Inthis case the maximum plunger force of the baling machine is usuallylimited by the maximum allowable drive torque of the drive train, whichis determined mainly by the design of the gearbox. This maximum drivetorque will provide a maximum plunger force that varies with theposition of the crank. In general the plunger force will be lowest whenthe angle between the crank and the plunger rod is approximately 90degrees and increases as the angle approaches 180 degrees.

During a compression cycle, the force exerted by the plunger istypically at a maximum at the moment when the bale material in thechannel starts to shift backward. At this moment the plunger is at adistance about equal to the wad thickness from the extended end positionof the plunger. During the shifting of the compressed material theplunger force will remain at a level that is slightly lower than themaximum force. Higher plunger forces will lead to a higher level ofcompression and a higher density of the bales.

In practice, there is an inverse relationship between the quantity ofbale material to be compressed on each compression stroke of the plungerand the maximum level of compression of the bale material and thedensity of the bale. If a large quantity of material is fed into thebale chamber this will result in a large wad thickness and a low levelof compression, and therefore a low density. On the other hand, if asmall quantity of bale material is fed into the bale chamber on eachstroke this will result in a small wad thickness and a high maximumlevel of compression, and therefore a high density. As the throughput ofthe baling machine (that is, the rate in kg/hour at which material iscompressed) depends on the amount of bale material compressed per strokeof the plunger, there is also an inverse relationship between thethroughput of the baler and the density of the bale. The operatortherefore has to choose either a high throughput and a low density, or alow throughput and a high density.

For the economical use of trucks for transporting the bales, bales of ahigh density are required. However, for fast processing of the balematerial, a high throughput is required. This creates a dilemma for theoperator, which has to compromise on the throughput of the baler and/orthe bale density. With a background art baler a higher density can onlybe achieved at high throughput by strengthening the gearbox, which addsto the cost of the baler.

BRIEF SUMMARY OF THE INVENTION

It is an object of the invention to mitigate at least one of theaforesaid problems. In particular, it is preferred object of theinvention to provide a baler and a method of baling that reduces thetorque within the drive line of the baler, thereby allowing an increasein the density of the bale without reducing the throughput or having tostrengthen the gearbox.

According to one aspect of the present invention there is provided abaler comprising a baling chamber that includes a bale-forming channelhaving an inlet end and an outlet end, a plunger mounted within thechannel for compressing bale material in the channel and driving thecompressed bale material towards the outlet end of the channel, and arotary drive mechanism for driving reciprocating movement of theplunger, wherein the baler includes an additional drive means fordriving the compressed bale material towards the outlet end of thechannel, said additional drive means being configured to drive thecompressed bale material towards the outlet end of the channel duringsuccessive compression cycles of the plunger, thereby reducing torque inthe rotary drive mechanism.

The present invention provides the advantage that the operator canselect a high throughput for the baling machine, and a high level ofcompression, without increasing the torque in the rotary drivemechanism. This allows the machine to produce high density bales withoutreducing the throughput or increasing the strength of the drive train.The invention thus avoids the problems described above, which resultfrom the fact that the plunger force varies with the position of thecrank arm of the drive mechanism.

Advantageously, the additional drive means is configured to engage oneor more side regions of the compressed bale material.

Advantageously, the additional drive means is configured forreciprocating movement, preferably for stepwise reciprocating movement.

Advantageously, the bale chamber comprises a plurality of panels formingthe top, bottom and sides of the channel, and the additional drive meansis configured to engage the compressed bale material through one or moreopenings in the panels.

Alternatively, the additional drive means comprises a secondary plungerconfigured for reciprocating movement within the baling chamber, whereinthe reciprocating movement of the plunger leads the reciprocatingmovement of the secondary plunger and the secondary plunger isconfigured to extend further than the plunger into the baling chamberduring a compression stroke.

Advantageously, the reciprocating movement of the plunger leads thereciprocating movement of the secondary plunger by a phase angle in therange 10 to 90 degrees, more preferably 20 to 60 degrees.

Advantageously, the plunger and the secondary plunger are configured tobe driven from a single rotary drive mechanism via respective primaryand secondary plunger rods.

Alternatively, they may be configured to be driven from separate rotarydrive mechanisms.

Advantageously, the additional drive means is configured to drive thecompressed bale material towards the outlet end of the channel betweenpoints of maximum compression force of the plunger during successivecompression cycles.

Advantageously, the additional drive means is configured to drive thecompressed bale material towards the outlet end of the channel by adistance equal to approximately half the wad thickness of the compressedbale material.

Advantageously, the additional drive means is configured to drive thecompressed bale material towards the outlet end of the channel by adistance in the range 20-60 mm, preferably 25-40 mm.

Advantageously, the additional drive means is adjustable to adjust thedistance that the compressed bale material is driven towards the outletend of the channel

Advantageously, the baler includes an adjustable friction controlelement comprising an adjustable panel of the bale-forming channel.Preferably the baler includes an actuator for adjusting a bias forceapplied to the adjustable panel.

Advantageously, the baler is an agricultural baler for baling anagricultural crop.

According to another aspect of the invention there is provided a methodof baling using a square baler comprising a baling chamber that includesa bale-forming channel having an inlet end and an outlet end, a plungermounted within the channel and a rotary drive mechanism for drivingreciprocating movement of the plunger, the method comprising loadingbale material into the baling chamber, compressing the bale material bydriving the plunger into channel, driving the compressed bale materialtowards the outlet end of the channel with the plunger, and additionallydriving the compressed bale material towards the outlet end of thechannel with an additional drive means during successive compressioncycles of the plunger, so as to reduce torque in the rotary drivemechanism.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

An embodiment of the invention will now be described by way of examplewith reference to the accompanying drawings, wherein:

FIG. 1 is an isometric view showing the main components of a backgroundart baling machine;

FIGS. 2-4 are schematic cross-sectional side views of the background artbaler, showing the baler in three different operational positions duringa baling operation;

FIGS. 5-9 are schematic cross-sectional side views of a baler accordingto a first embodiment of the invention, showing the baler in fivedifferent operational positions, and

FIGS. 10-14 are schematic cross-sectional side views of a baleraccording to a second embodiment of the invention, showing the baler infive different operational positions.

DETAILED DESCRIPTION OF THE INVENTION

The background art baling machine or baler shown in FIGS. 1-4 isconfigured to be pulled over a field and driven by a tractor (notshown). Alternatively, the baler could be self-propelled and/orself-driven.

The baler includes a baling chamber C and a plunger D that can be driveninto the baling chamber C in a reciprocating manner. The baling machinealso includes a pick up mechanism M for picking up cut bale materialsuch as grass and straw from the ground, a feed mechanism N for feedingthe bale material into the baling chamber C and a driveline X fortransmitting drive to the plunger D from the drive output of a towingvehicle (not shown).

These components are all conventional and may for example be asdescribed in U.S. Pat. Nos. 4,074,623 and 4,142,746. The baling machinealso includes a binding device E for binding the bale with bindingtwine. This binding device may for example be as described in U.S. Pat.No. 4,074,623.

The baling chamber C comprises an open ended bale-forming channel Athrough which compressed bale material 1 is forced by the reciprocatingplunger D. In this example, the plunger D is driven from a rotatingdrive axle 2 via a crank 8 and the plunger rod 3. The drive axle 2comprises an output shaft of a drive gearbox 5 that also has a driveinput shaft 4 through which it receives drive from the drive output of atowing vehicle (not shown). The gearbox 5 is mounted on a frame 7 of thebaling machine. The drive input shaft carries a large flywheel 9 forsmooth operation of the baler.

Typically the material to be baled is taken up from the ground by thepick-up device M. The feed device N feeds the material to anintermediate material buffer 10. The feed device N may be equipped withknives 12 for cutting up the material to be baled. When sufficientmaterial has collected in the intermediate buffer 10, a stuffer 11forwards the material into the bale chamber C in front of the plunger D.The material is then ready to be compressed.

The open ended channel A that forms the baling chamber C has an inletend 13 and an outlet end 14. The bale-forming channel A is defined bytwo side panels 15 (one of which has been omitted in FIG. 1 to show theinterior of the baling chamber C), a top panel 16 and a bottom panel 17.The top panel 16 (and/or one or both of the side panels 15) may comprisean adjustable panel that is pivotable about its upstream end allowingthe cross-sectional area of the bale-forming channel A to be adjusted.An adjusting mechanism 18 for adjusting the position of the adjustablepanel 16 is provided towards the outlet end 14 of the baling chamber C.The adjusting mechanism 18 applies a biasing force F to the adjustablepanel 16, to control the level of friction between the panel and thecompressed material 1 in the baling chamber C. The adjustable panel 16thus comprises a friction control element.

The plunger D is driven in a substantially linear direction L in thelongitudinal direction of the baling chamber between two end positionscomprising respectively a withdrawn position (FIG. 2) in front of thebaling chamber C and an extended position (FIG. 4) in which it extendsinto the channel A of the baling chamber C. When the plunger is in thewithdrawn position (FIG. 2) the baling chamber C is loaded with the balematerial to be compressed. The plunger D is then driven into the balingchamber so that this new bale material is first shifted into contactwith a body of compressed material 1 already in the baling chamber C andthen compressed against that body of material. The newly compactedmaterial forms a wad W that is added to the already compacted material 1in the channel A. The friction of the compressed material 1 with thepanels 15, 16, 17 of the baling chamber C provides a resistive forceallowing for compression of the new material that is introduced into thebaling chamber C in front of the plunger D.

After compression, continued movement of the plunger D drives the wad Wof newly compressed material and the compressed material 1 already inthe baling chamber C towards the outlet end 14 of the baling chamberuntil the plunger D reaches its fully extended end position. The plungerD then returns in the opposite direction to its withdrawn position sothat the baling chamber C can be reloaded with new material to becompressed. The plunger therefore performs a compression cycle thatconsists of a compression stroke followed by a return stroke. Thiscompression cycle is repeated continuously until the baling process isfinished.

A bale 1 b is formed from the compressed material in the baling chamberand bound with twines 19 that are looped around the body of compressedmaterial in order to hold it in compression after leaving the balingmachine. This binding process can be performed as follows.

At the start of the baling process two lengths of twine from spools (notshown) on opposite sides of the baling chamber C are connected to oneanother by tying the ends of the twines together using the bindingdevice (or knotter) E. As the bale material is compacted in the balingchamber C the spools feed twine to the baling chamber C on either sideof the bale material. On one side of the baling chamber C the twinepasses through the tip of a baling needle 20. When the body ofcompressed bale material 1 has reached its full length, between twosuccessive compressing strokes, the needle 20 brings the twine as a loopto the other side of the baling chamber C. The knotter E then knots thetwine, joining an end of the twine loop that was brought around thecompressed bale by the needle 20 to an end of the twine that wassupplied by the spool on other side of the baling chamber (the same sideas the knotter device E). The needle 20 is then retracted and a new baleis started.

During a compression cycle, the force exerted by the plunger D istypically at a maximum at the moment when the newly fed bale materialhas been compressed and the bale material 1 already in the channel Astarts to shift backwards (FIG. 3). At this moment the plunger is at adistance about equal to the wad thickness d from the extended endposition of the plunger. During the shifting of the compressed materialthe plunger force will remain at a level that is slightly lower than themaximum force.

The maximum plunger force of the baling machine is limited by themaximum allowable drive torque of the drive train. This maximum drivetorque will provide a maximum plunger force that varies with theposition of the crank. For example, as illustrated in FIG. 3, if thegearbox 5 has a maximum drive torque of 90.000 Nm and the crank 8 has alength of 360 mm, the maximum plunger force will be about 250.000 N whenthe angle A between the crank 8 and the rod 3 is about 90 degrees, andabout 750.000 N when the angle A between the crank and the rod is 160degrees.

The invention describes a method and apparatus that reduces the torquerequired for the drive line of a baler, thereby allowing an increase inthe density of the bale without having to strengthen the gearbox.

FIGS. 5-9 illustrate a baler according to a first embodiment of theinvention. This baler is similar to the background art baler describedabove and shown in FIGS. 1-4, except as described below.

In the first embodiment of the invention, additional drive means 22 areprovided within the bale channel A that engage the side regions of thecompressed bale material 1 in the bale channel A. Preferably, theadditional drive means 22 are located close to the inlet end 13 of thebale channel A but backward of the fully extended position of theplunger D at the end of the compression stroke.

In this embodiment, two additional drive means 22 are provided, whichextend through openings in the top and bottom panels 16, 17 of thebaling chamber C. Alternatively or in addition, additional drive meansmay be associated with the side panels 15. The additional drive means 22could if required be integrated with one or more ejection devices forejecting a final bale and cleaning the channel after baling of the balematerial in a field has been completed.

Each additional drive means 22 consists of a set of tines 23 and anactuator 24 that causes the tines 23 to reciprocate with a steppingmotion in the longitudinal direction of the channel A in order to shiftthe compacted bale material rearward towards the outlet end 14 of thechannel A. This stepping motion consists of the following movements: (i)the tines 23 are introduced transversely into the baling chamber C asshown in FIG. 5; (ii) the tines 23 are driven rearwards in thelongitudinal direction S towards the outlet end 14 of the baling chamberas shown in FIG. 6; (iii) the tines 23 are withdrawn transversely fromthe baling chamber C as shown in FIG. 7, and (iv) the tines 23 arereturned to the start position by moving them in the longitudinaldirection towards the inlet end 13 of the baling chamber, as shown inFIGS. 8 and 9. The actuator 24 may for example be mechanically,electrically or hydraulically driven.

During operation, the additional drive means 22 engage the side regionsof the already compressed bale material 1 in the baling chamber C. Thestepping motion is coordinated with the motion of the plunger D so thatthe bale material is shifted rearwards by the additional drive means 22during successive compression cycles of the plunger D. Morespecifically, the additional drive means 22 are configured to drive thecompressed bale material towards the outlet end of the channel at a timebetween points of maximum compression force of the plunger D. As aresult, maximum compression takes place later in the plunger stroke,when the angle A between the crank 8 and the plunger rod 3 is larger.This allows the plunger D to exert a large plunger force withoutexceeding the torque limit of the drive train X.

The additional drive means 22 do not act on the bale material during thefinal part of the plunger compression stroke when, owing to the positionof the crank 8, the plunger D is able to exert a maximum compressionforce on the bale material without exceeding the torque limit of thedrive train.

Operation of the baler is substantially as described above in relationto the background art baler shown in FIGS. 1-4, except for the use ofthe additional drive means 22. The operation of the additional drivemeans 22 during a baling operation will now be described in more detailwith reference to FIGS. 5-9.

In FIG. 5 the baler is shown at the start of a compression stroke. Theplunger D is in a fully retracted position, leaving an empty space atthe inlet end 13 of the baling chamber C. Bale material is lifted fromthe intermediate buffer 10 into this space in the baling chamber C bythe stuffer 11. The tines 23 have already been introduced transverselyinto the baling chamber C by the actuator 24.

In FIG. 6 the baler is shown during a first part of the compressionstroke. The plunger D has started moving into the baling chamber C toshift the newly-introduced bale material towards the body of compressedmaterial 1 already in the chamber. At the same time, the tines 23 of theadditional drive means 22 are being driven rearwards by a distance S inthe longitudinal direction L, thereby driving the compressed material 1towards the outlet end 14 of the baling chamber. The amount of shifting(i.e. the movement) of the compressed material in the baling chamber Cprovided by the additional drive means 22 is preferably less than theaverage shifting movement produced by the plunger D during a compressionstroke.

As a result of this backward shifting of the compressed bale material,compression of the newly introduced bale material against the body ofcompressed material does not take place until later in the compressionthan would have been the case with no additional shifting. Maximumcompression therefore takes place at a larger value of the angle Abetween the crank arm 8 and the plunger rod 3. This reduces the torquein the drive train X.

In FIG. 7 the baler is shown during a final part of the compressionstroke. The plunger D has moved nearly to its full extension into thebaling chamber C, thus compressing the wad W of bale material in thechamber C. The tines 23 of the additional drive means 22 have beenremoved from the baling chamber. At this point the force applied by theplunder D is at a maximum and the compressed bale material 1 starts toslide with the completed bale 1 b towards the outlet end 14. The angleA2 between the crank arm 8 and the plunger rod 3 is now very large(typically between 140 and 180 degrees), producing a large plunger forcewithout exceeding the maximum allowed torque of the drive train.

In FIG. 8 the baler is shown at the end of the compression stroke. Theplunger D has moved fully into the baling chamber C. The tines 23 of theadditional drive means 22 are returning to their starting positiontowards the inlet end of the baling chamber. The compressed balematerial 1 and the completed bale 1 b have finished sliding towards theoutlet end 14.

Finally, in FIG. 9 the baler is shown during the return stroke. Theplunger D is moving back towards its fully retracted position and thestuffer 11 is preparing to introduce another load of bale material intothe baling chamber C. The tines 23 of the additional drive means 22 areready to be reintroduced into the baling chamber for the nextcompression stroke.

Because of the additional shifting S of the material in the bale channelA (FIG. 6), the maximum force for the plunger D occurs at an angle A2(FIG. 7) between crank 8 and plunger rod 3 that is bigger than the angleA of maximum force (FIG. 3) in the background art mechanism where noadditional shifting is done. As a result, less torque on the drivelineof the crank is required. For comparison, FIG. 3 shows the angle A ofmaximum force without the additional shift produced by the additionaldrive means, and FIG. 7 shows the angle A2 of maximum force with theadditional shift.

It should be understood that the shifting produced by the additionaldrive means 22 may take place at any time during the compression cyclebetween points of maximum compression force of successive compressionstrokes of the plunger. For example, the shifting may take place duringa first part of the compression stroke as described above, or while theplunger is returning to its fully withdrawn position, or at any otherpoint during the compression cycle, apart from at the time of maximumcompression during the final part of the compression stroke.

The additional drive means 22 is preferably configured to drive thecompressed bale material towards the outlet end of the channel by adistance equal to approximately half the wad thickness of the compressedbale material. Typically, this will be a distance in the range 20-60 mm,or more usually 25-40 mm, depending on the wad thickness. The additionaldrive means 22 may be adjustable to adjust the distance that thecompressed bale material is driven towards the outlet end of thechannel.

FIGS. 10-14 illustrate a baler according to a second embodiment of theinvention. This baler is similar to the background art baler describedabove and shown in FIGS. 1-4, except as described below.

The baler shown in FIGS. 10-14 has a two-part plunger comprising a lowerplunger D1 and an upper plunger D2. Alternatively, the plunger could bedivided horizontally into left and right plunger parts. In thisembodiment, the lower and upper plungers D1, D2 are driven from a commoncrank 8 via respective plunger rods 3 a, 3 b. Alternatively, the lowerand upper plungers D1, D2 could be driven from separate cranks.

Owing to the arrangement of the plunger rods 3 a, 3 b there is a phasedifference in the reciprocating movement of the two parts of the plungerduring operation of the baler, which in this embodiment is equal to aphase angle of approximately 35 degrees. In this embodiment the crank 8rotates anti-clockwise and as a result the lower plunger D1 leads andthe upper plunger D2 follows. The plunger rods 3 a, 3 b are different inlength, the upper plunger rod being longer so that at maximum extensionthe upper plunger D2 extends further into the baling chamber than thelower plunger D1. Alternatively or in addition the same result can beachieved by making the upper plunger D2 longer than the lower plungerD1. More generally, the following plunger is configured to extendfurther into the baling chamber than the leading plunger during acompression stroke.

The method of operation is similar to that of the background art balerdescribed above and shown in FIGS. 1-4, except that the lower and upperplungers D1, D2 act in a time shifted fashion and the following plungerthat comes in later in the cycle (in this example the upper plunger D2)has an end position further towards the end of the bale channel A thanthe end position of the leading plunger (here, the lower plunger D1).This causes the compacted bale material 1 to be shifted further towardsthe outlet end 14 of the bale chamber C than would have been the case ina baler having a single plunger, for example as illustrated in FIGS.1-4.

Preferably, the end position of the following plunger is located furtherinto the bale channel than the end position of the leading plunger by adistance equal to about half of the average compacted wad thickness T.Typically, the wad thickness is between 50 mm and 80 mm and the distancebetween the end positions of the leading and following plungers in therange 20-60 mm, more usually 25-40 mm. Optionally, the plunger rods 3 a,3 b and/or the lengths of the plungers D1, D2 may be adjustable toadjust the distance between the end positions of the leading andfollowing plungers.

The later-acting following plunger constitutes an additional drive meanswhich helps to reduce the torque in the drive train. Therefore, in thisembodiment the upper plunger D2 constitutes the additional drive means,which acts on the bale material to reduce the torque during compressionof the bale material by the lower plunger D1. This will now be explainedwith reference to the sequence of operation shown in FIGS. 10 to 14.

When the lower and upper plungers D1, D2 are in their most forward(withdrawn) positions as shown in FIG. 10 the bale material to becompressed is fed by the stuffer 11 into the inlet end 13 of the balechamber C in front of the plungers D1, D2.

In FIG. 11 the baler is shown during a first part of the compressionstroke. The lower plunger D1 and the upper plunger D2 have both startedadvancing into the bale chamber C, but the lower plunger D1 has advancedfurther than the upper plunger D2 owing to the phase difference betweenthe plungers. The bale material in the lower part of the chamber C isthus compressed by the lower plunger D1 against the compacted balematerial 1 already in the chamber C. Because the already compacted balematerial is located further away than the end position of the lowerplunger D1, the angle between the crank 8 and the first plunger rod 3 ais bigger than it would have been if the compacted material were locatedat the end position of the lower plunger. Therefore the torque requiredfor driving the earlier-acting lower plunger D1 is reduced.

In FIG. 12 the baler is shown with the lower plunger D1 at maximumextension into the baling chamber C. The upper plunger D2 is stilladvancing into the chamber C and before the upper plunger D2 fullycompresses the bale material in the upper part of the chamber, the lowerplunger D1 shifts the newly compacted bale material and the alreadycompacted material 1 rearwards along the bale channel A by a distance½T.

In FIG. 13 the baler is shown a little later in the compression cycle.The lower plunger D1 has started to withdraw from its maximum extensioninto the baling chamber C and the upper plunger D2 is still advancinginto the chamber C. The later-acting upper plunger D2 further compactsthe newly entered bale material against the already compacted material1. As this material has already been shifted a distance ½T by the lowerplunger D1 towards the outlet of the channel A, the angle between thecrank 8 and the plunger rod 3 b at which the upper plunger D2 provides amaximum force is larger than it would have been if there was no shiftproduced by the lower plunger D1. Thus, the upper plunger D2 alsorequires a lower drive torque to provide the maximum plunger force.

In FIG. 14 the baler is shown at the moment when the upper plunger D2reaches maximum extension into the baling chamber C. The upper plungerD2 has shifted the compacted material 1 rearwards in the bale channel Aby a further distance ½T. The lower and upper plungers D1, D2 have thusshifted the compressed bale material by a total distance T during thecourse of a complete compression stroke. The lower plunger D1 hasretracted further from the chamber C towards the start position at theinlet end of the chamber. Both plungers D1, D2 then return to the startposition shown in FIG. 10 and the cycle repeats.

A practical advantage of the invention is that the operator can choose ahigh throughput for the baling machine, while maintaining a high levelof compression and a high density of the bales, without exceeding totorque limit of the drive train.

Various modifications of the invention are of course possible. Forexample, in the first embodiment shown in FIGS. 5-9 the reciprocatingadditional drive means 22 that engages side regions of the compressedbale material 1 may be replaced by other drive means, for examplerotating rollers, wheels, chains or belts. In the second embodimentshown in FIGS. 10-14 the lower and upper plungers D1, D2 may be replacedby plungers mounted side-by-side or one within the other, for examplecoaxially.

The invention claimed is:
 1. A baler comprising: a baling chamber that includes a bale-forming channel having an inlet end and an outlet end; a plunger mounted within the channel for compressing bale material in the channel and driving the compressed bale material towards the outlet end of the channel; and a rotary drive mechanism for driving reciprocating movement of the plunger to a first end position within the channel, wherein the baler includes an additional drive means comprising a secondary plunger for driving the compressed bale material towards the outlet end of the channel, wherein the secondary plunger is configured for reciprocating movement to a second end position within the channel, wherein the reciprocating movement of the plunger leads the reciprocating movement of the secondary plunger and wherein the second end position is located further towards the outlet end of the channel than the first end position, whereby the secondary plunger is configured to extend further than the plunger into the channel during a compression stroke, the secondary plunger being configured to drive the compressed bale material towards the outlet end of the channel during successive compression cycles of the plunger, thereby reducing torque in the rotary drive mechanism.
 2. A method of baling using a baler comprising a baling chamber that includes a bale-forming channel having an inlet end and an outlet end, a plunger mounted within the channel and a rotary drive mechanism for driving reciprocating movement of the plunger to a first end position within the channel, the method comprising: loading bale material into the baling chamber; compressing the bale material by driving the plunger into channel; driving the compressed bale material towards the outlet end of the channel with the plunger; and additionally driving the compressed bale material towards the outlet end of the channel with an additional drive means comprising a secondary plunger during successive compression cycles of the plunger, so as to reduce torque in the rotary drive mechanism, wherein the secondary plunger is configured for reciprocating movement to a second end position within the channel, and wherein the reciprocating movement of the plunger leads the reciprocating movement of the secondary plunger and wherein the second end position is located further towards the outlet end of the channel than the first end position, whereby the secondary plunger extends further than the plunger into the channel during a compression stroke.
 3. The baler according to claim 1, wherein the plunger and the secondary plunger are configured to be driven from a single rotary drive mechanism via respective primary and secondary plunger rods.
 4. The baler according to claim 1, wherein the secondary plunger is configured to drive the compressed bale material towards the outlet end of the channel between points of maximum compression force of the plunger during successive compression cycles.
 5. The baler according to claim 1, wherein the secondary plunger is configured to drive the compressed bale material towards the outlet end of the channel by a distance in a range of 20-60 mm.
 6. The baler according to claim 1, wherein the secondary plunger is adjustable to adjust the distance that the compressed bale material is driven towards the outlet end of the channel.
 7. The baler according to claim 1, including an adjustable friction control element comprising an adjustable panel of the bale-forming channel.
 8. The baler according to claim 1, wherein the baler is an agricultural baler for baling an agricultural crop.
 9. The baler according to claim 1, wherein the secondary plunger is configured to drive the compressed bale material towards the outlet of the channel by a distance in a range of 25-40 mm. 